The present invention relates to a method for purification of vinyl polymers, vinyl polymers, hydrosilylatable compositions, and curable compositions.
The hydrosilylation reaction is used for functional group transformation or crosslinking, for instance, and as such is one of reactions of great industrial importance. By way of illustration, it is known that a polymer having an alkenyl functional group at its molecular chain terminus undergoes crosslinking in the presence of a hydrosilyl group-containing compound as a curing agent to give a cured product of good heat resistance and durability and that the reaction of such an alkenyl group-terminated polymer with a crosslinkable silyl group-containing hydrosilyl compound gives a crosslinkable silyl group-terminated polymer. While such a hydrosilylation reaction proceeds under heating, a hydrosilylation catalyst is generally added for accelerating the reaction. As examples of said hydrosilylation catalyst, radical initiators, such as organic peroxides and azo compounds, and transition metal catalysts can be mentioned. It is known that particularly when a transition metal catalyst is used, the hydrosilylation reaction can be promptly carried to completion with no more than the so-called catalyst amount of the catalyst.
Meanwhile, as a technology for precision synthesis of polymers, the living polymerization method is generally known. Living polymerization not only provides for effective control of molecular weight and molecular weight distribution but gives a polymer with a definite terminal structure. Therefore, living polymerization can be cited as an effective method for introduction of a functional group into the polymer chain terminus. Recently polymerization systems suited to living polymerization have been discovered in the field of radical polymerization as well and studies on living radical polymerization are have been undertaken with a great enthusiasm. Particularly by utilizing the atom transfer radical polymerization technique, a vinyl polymer with a narrow molecular weight distribution can be obtained. As an example of the atom transfer radical polymerization technique, there can be mentioned a polymerization system using an organohalogen compound or a halogenated sulfonyl compound as the initiator and a metal complex the center metal of which is an element of group 8, group 9, group 10 or group 11 of the periodic table of the elements as a catalyst [e.g. Matyjaszewski et al., J. Am. Chem. Soc. 1995, 117, 5614, Macromolecules 1995, 28, 7901, Science 1996, 272, 866 or Sawamoto et al., Macromolecules 1995, 28, 1721].
However, the vinyl polymer produced by atom transfer radical polymerization contains residues of the transition metal complex used as the polymerization catalyst, so that troubles such as discoloration and adverse effects on physical properties of the product polymer as well as environmental safety problems are at times encountered. Taking an alkenyl group-terminated vinyl polymer produced by utilizing said atom transfer radical polymerization technique as an example, the residual catalyst acts as a catalyst poison in hydrosilylation to interfere with the hydrosilylation reaction so that the expensive transition metal catalyst has to be used in a substantial amount.
The inventors of the present invention discovered that an increased hydrosilylation activity could be assured by contacting the vinyl polymer obtainable by atom transfer radical polymerization with an adsorbent for purification (Japanese Kokai Publication Hei-11-193307). However, this practice tends to require a large quantity of the adsorbent entailing an increased burden on the environment associated with the subsequent disposal of the adsorbent and an increased production cost. The present invention overcomes the above problems and provides an economical and efficient method for purification of vinyl polymers, hydrosilylatable polymers and relevant compositions.
(1) The present invention is concerned with a method for purification of a vinyl polymer obtainable by the atom transfer radical polymerization of a vinyl monomer using a transition metal complex as a polymerization catalyst, wherein an oxidizing agent or a reducing agent is used.
(2) The invention is further concerned with a method for purification of a vinyl polymer having at least one alkenyl group per molecule or an intermediate obtainable in the course of production of said vinyl polymer, wherein an oxidizing agent or a reducing agent is used.
(3) The invention is further concerned with a purification method wherein said vinyl polymer having at least one alkenyl group per molecule is obtainable by the atom transfer radical polymerization of a vinyl monomer using a transition metal complex as a polymerization catalyst.
(4) The invention is further concerned with a method for purification of a vinyl polymer for use as a component constituting a hydrosilylatable composition, wherein the use of an oxidizing agent or a reducing agent is used.
(5) The invention is further concerned with a vinyl polymer obtainable by any of the above purification methods (1) to (4) and a hydrosilylatable composition comprising said polymer.
(6) The invention is further concerned with a curable composition comprising (A) an alkenyl group-containing vinyl polymer obtainable by any of the above purification methods (1) to (4) and (B) a compound containing at least 1.1 hydrosilyl groups per molecule.
(7) The invention is further concerned with a crosslinkable silyl group-containing vinyl polymer obtainable by subjecting an alkenyl group-containing vinyl polymer obtainable by any of said purification methods (1) to (4) and a hydrosilyl group-containing compound additionally having a crosslinkable silyl group to hydrosilylation reaction.
(8) The invention is further concerned with a curable composition comprising said crosslinkable silyl group-containing vinyl polymer.